The present invention relates to a device for driving a light source such as a semiconductor light-emitting element, in particular a semiconductor laser diode (LD), in such a way that it outputs light (laser light) of very short pulses having duration of several tens of picoseconds at a desired repetition frequency.
In order to produce laser light of very short pulses having duration of several tens of picoseconds from laser diodes, the latter must be supplied with electric pulses having duration of several hundreds of picoseconds. Such short electric pulses are commonly produced by utilizing the avalanche breakdown of avalanche transistors or with comb generators.
The repetition frequency of avalanche transistors is limited to about 100 kHz by the recovery time of avalanche breakdown and the charge time required to build up a high voltage. On the other hand, with comb generators, the repetition frequency of more than 1 GHz can be obtained, but the use of a resonance circuit precludes operation at variable repetition frequencies.
There is another type of a drive device which can produce such short electric pulses at variable repetition frequencies by utilizing the abrupt reverse current cut-off characteristic of a step-recovery diode. However, in this device the upper limit of the repetition frequency is about 10 MHz.